What is the speed of computer?

The speed can be determined in various ways. The clock speed of the processor, the speed of the hard drive, the speed of the bus carrying information from the processor to the memory and the speed of the memory.

dual or quad core processors running at more than 2.5 Ghz is fast

a hard drive that has a spindle speed of 7500 to 10,000 RPMs is fast

1066 or 2000 Mhz of front side bus is fast

800 Mhz or more memory speed is fast